This disclosure relates to a process to prepare high heat polycarbonate compositions, and in particular a process to prepare high heat polycarbonate copolymer compositions.
Polycarbonates are widely used thermoplastic polymers owing to their superior impact resistance, transparence and good resistance to thermal deformation at elevated temperatures. Most commercial polycarbonate is the homopolycarbonate of bisphenol A (“BPA”) and has a glass transition temperature in the range of 135 to 155° C. So-called high heat polycarbonates include copolymers of BPA with 3,3-bis(4-hydroxyphenyl)-2-phenylisoindolin-1-one (“PPPBP”) which have glass transition temperatures above the homopolycarbonate of BPA.

To improve the glass transition temperature of a polycarbonate, blends of BPA polycarbonate with copolymers containing units derived from PPPBP can be made. Thus, there is a desire to prepare copolymers with relatively high levels of PPPBP units, as these materials provide the most flexibility for blending with BPA polycarbonate to produce intermediate compositions.
Several synthetic routes have been reported for the synthesis of random PPPBP/BPA copolymers, but no single process works best for all compositions. PPPBP/BPA copolymers are less hydrolytically stable than BPA polycarbonate, and the hydrolytic instability increases with increasing PPPBP loading. Copolymers with compositions above 70 mole % PPPBP are particularly unstable.
Melt polymerization routes to PPPBP/BPA copolymers based on diphenyl carbonate (“DPC”) require long residence times at high temperatures and can lead to higher color. These polymerizations become even more difficult as the PPPBP loading increases. Melt polymerizations of PPPBP/BPA copolycarbonates using DPC as the carbonate source are particularly unfavorable when the PPPBP content exceeds 30 mole %, as the required reaction temperatures can approach the decomposition temperature of the product polymers.
Melt polymerization using bis(methyl salicylate)carbonate (“BMSC”) as the carbonate source reduces the residence time required at high temperatures and allow production of copolymers with >30 mole % PPPBP, but BMSC is not available at large scale and is not a viable commercial option. High color in the resulting polymer also remains an issue.
Interfacial polycarbonate polymerizations are low temperature processes and are particularly advantageous for the synthesis of high temperature polycarbonates. Interfacial polymerizations of PPPBP/BPA copolymers produce lower color polymer and are the commercially preferred route to PPPBP/BPA copolymers, but even interfacial polymerizations of PPPBP/BPA copolymers can suffer from processing issues. Standard interfacial polycarbonate manufacturing processes use centrifuge trains to separate aqueous impurities from the organic polymer stream. Interfacial polymerization of PPPBP/BPA copolymers can result in polymer solutions that separate poorly from the aqueous streams. Mixing of these organic and aqueous streams under shear can lead to emulsification (known as “creaming”), which results in yield loss and lower purity polymer. The presence of residual impurities in the polymer can result in reduced hydrolytic stability.
A known interfacial bischloroformate route to random PPPBP/BPA copolymer was found to be most effective at relatively low (<30 mole %) PPPBP loadings. Bischloroformate routes to PPPBP copolymers are not preferred for large scale manufacturing as they are less robust, more expensive, and less efficient from an economic standpoint because they often result in low throughput rates. Bischloroformate routes are highly sensitive to ppm levels of residual catalysts belonging to the family of alkylamines, and can result in high polydispersity especially at high pH.
Interfacial routes to PPPBP/BPA copolycarbonate have been reported based on the use of phosgene as the carbonate source and an amine-catalyzed ammonium salt phase-transfer catalyzed interfacial process. These routes produced random PPPBP/BPA copolymer, but suffer from various amounts of centrifuge creaming and suboptimal hydrolytic stability of the resulting polymer.
There accordingly remains a need in the art for a robust, efficient, and cost effective process for the production of random PPPBP/BPA copolymers with high loading of PPPBP, e.g. about 30 to about 70 mole % PPPBP having low creaming and resulting in polymers having improved hydrolytic stability.